Mechanical waves are waves that require a medium. This means that they have to have some sort of matter to travel through. These waves travel when molecules in the medium collide with each other passing on energy. One example of a mechanical wave is sound. Sound can travel through air, water, or solids, but it can't travel through a vacuum. It needs the medium to help it travel. Other examples include water waves, seismic waves, and waves traveling through a spring.
Hi Kelly, I'm now 28 weeks pregnant with twins and I first started feeling them move when I was around 15/16 weeks pregnant but this is my second pregnancy. In my first pregnancy (not twins) I didn't feel any movement until I was 24 weeks pregnant. I think everyone feels their babies at different times so don't worry about anything.
For most women, they wonât feel the babyâs first movements until the second trimester â sometime between 16 and 22 weeks pregnant. If this is your first pregnancy, you may not feel your babyâs subtle fetal movements (called quickening in pregnancy) until 22 weeks pregnant. Women who have been pregnant before tend to feel their babyâs movements earlier than first-time moms.